In recent years, there is an increasing need of a gasket that is exposed to a temperature of from 600 to 800° C., but the following problems are involved. An SUS301 or SUS431 series material represented by those described in PTLs 1, 2, and 3 undergoes significant softening since the heating temperature is close to the decomposition temperature of the martensite phase, and thus is inferior in settling resistance. A precipitation strengthened material, such as NCF 625 and NCF 718 defined in JIS G4902 (corrosion-resisting and heat-resisting superalloy plates and sheets) and SUH660 defined in JIS G4312 (heat-resisting steel plate), is effective for precipitation strengthening at a temperature of from 600 to 800° C., but the cost thereof is increased due to expensive Ni contained in a large amount. PTLs 4, 5, 6, and 7 describe an Fe—Cr—Mn—Ni austenitic stainless steel strengthened by Ni, which is being applied to a part of heat resistant gaskets.
The aforementioned steel species have been studied for further enhancing the high strength thereof, assuming the use thereof in a high temperature range. However, in the case where a large amount of a martensite phase is contained, and in the case where the N content is large, the yield stress (0.2% offset yield strength) is significantly increased. Furthermore, a material that has been increased in strength by cold rolling finishing (which is hereinafter referred to as an “HT material”) is generally applied to a gasket, and thus the gasket suffers surface roughening on forming, and suffers necking at a bent part in the case where the ductility thereof is insufficient. These surface property and defects in the processed shape become a factor of considerable deterioration in gas sealing capability.